The present invention relates to a novel illumination system that includes several gas discharge tubes. The present invention also relates to a novel power supply for the illumination system.
Lighting systems for indoor and outdoor illumination of advertising signs and for other purposes have been used for many decades. An illumination system may include several gas discharge tubes, such as cold cathode tubes or fluorescent tubes. A cold cathode tube is a sealed glass tube that is filled with inert gas, such as argon or neon, wherein different ionized gases provide light of different colors. A fluorescent tube is a sealed glass tube having its inner walls coated with phosphorus and the tube is filled with, for example, mercury vapor. Both types of tubes may be fabricated in many different shapes and sizes. The tubes include electrodes connected to a high-frequency, high-voltage power supply that provides a striking voltage and a running voltage. The gas inside the tubes is ionized so that the gas atoms or molecules are stimulated to emit light of a known wavelength. To ionize the inert gas, a striking voltage of approximately 1.5 times the running voltage is required. Once ionized, a constant current is preferably maintained across the gas tube at a running voltage. The striking and running voltages are proportional to the tube length and are typically in the range of several hundred to several thousand Volts. The luminous intensity of the ionized gas is proportional to the current that flows between the electrodes inside the tube.
For advertising purposes, each gas discharge tube may be located within a letter enclosure. The letter enclosure may be shaped in the form of a letter or may have a rectangular shape with a letter sign in front of the gas discharge tube. The effectiveness of an advertising sign also depends on having letters of various shapes and sizes emitting light of a selected intensity, which is usually equal for all letters. Typically, the individual gas discharge tubes are powered by high-frequency, high-voltage power supplies. The output from each power supply is connected to the tube electrodes using high-voltage GTO cables. These high-voltage cables require special installation and can have only a limited length due to safety requirements. To install an outside sign, each letter may require two GTO cables located in two separate and relatively large holes drilled through an external wall. Thus, installing a large number of letters or symbols may require a significant amount of time and possibly damage to the wall.
There is still a need for an illumination system that includes several gas discharge tubes, is easy to install and operates efficiently.
The present inventions relate to an illumination system and method for providing electrical power to several gas discharge tubes and for controlling operation of the gas discharge tubes. The present inventions also relate to a novel high-frequency power converter, and detection and control modules used in the above system. The detection module and a method detect one or several conditions occurring during the operation of an illumination system, including operation and fault conditions, such as an open circuit state, a short circuit state, an output loading state, a ground fault state, an inverter fail state, or a line over-voltage state.
The present invention also relate to a high-frequency low-voltage power supply arranged to operate with a plurality of high-voltage modules, wherein each high-voltage module is constructed to provide electrical power to at least one gas discharge tube. The high-voltage modules may be located several hundred feet away from the power supply. The power supply may be a high-frequency current source with a high power factor design. Upon detecting a fault condition, the power supply automatically shuts-off power generation. The present invention also relates to a high-voltage module connectable in series with other high-voltage modules and each arranged to provide high-frequency and high-voltage electrical power to a gas discharge tube.
According to one aspect, a system for providing electrical power to several gas discharge tubes includes a master power supply and several high-voltage modules. The master power supply is constructed and arranged to provide high-frequency and low-voltage power to the high-voltage modules. Each high-voltage module, in turn, provides high-frequency and high-voltage power to a gas discharge tube. The high-voltage modules include step-up transformers with their primary sides connected in series to the output of the master power supply and their secondary sides connected to the gas discharge tubes.
According to another aspect, a method for providing electrical power to several gas discharge tubes includes generating a high-frequency and low-voltage power signal, providing the high-frequency and low-voltage power signal via a standard electrical wire (e.g., 3 leadxc3x9714 AWG wire) to several high-voltage modules. Each high-voltage module includes a step-up transformer with a primary side and a secondary side. The method also includes receiving the high-frequency and low-voltage power signal by the high-voltage modules having the primary sides connected in series, and providing a high-frequency and high-voltage power signal from the secondary sides to the gas discharge tubes.
The system for providing electrical power may include one or more of the following. The master power supply includes an inverter type power supply. The master power supply includes a power inverter connected to an AC output current source via a transformer. The power inverter includes two bipolar transistors arranged as a Darlington pair for providing a high current gain.
The master power supply includes a ground fault detector connected to ground fault feedback circuits located in the high-voltage modules. The master power supply includes an open circuit detector. The master power supply includes a broken tube level sensor. The master power supply includes an H.F. converter output loading detector. The master power supply includes an anti-bubble circuit constructed and arranged to superimpose a square wave signal of a low-frequency onto the high-frequency and low-voltage power provided by the master power supply to the high-voltage modules. The master power supply includes an inverter fail detector. The master power supply includes a line over voltage detector. The master power supply includes a control module. The control module includes a CPU fault manager. The CPU fault manager is connected to a diagnostic indicator. The CPU fault manager is connected to a telemetry module.
According to yet another aspect, in a system for providing electrical power to several gas discharge tubes, one high-voltage module may be connectable in series with another high-voltage module. The high-voltage modules include step10 up current transformers having primary sides, connectable together in series and to an output of an inverter type power supply, and secondary sides connectable to a gas discharge tube.
The high-voltage module may include a ground fault feedback circuit constructed and arranged to provide a ground fault feedback signal to a ground fault detector. The ground fault feedback circuit may include a discharge resistor connected in parallel to a first capacitor, wherein the discharge resistor and the first capacitor are connected between an input return of the primary side and a high-voltage return of the secondary side. The ground fault feedback circuit may further include a second capacitor connected to the high-voltage return between the secondary side and the gas discharge tube. The ground fault feedback circuit further includes a third capacitor connected between the high-voltage return and a chassis ground connection. The ground fault feedback circuit includes only passive elements.
The high-voltage module may include a voltage limiter connected across the primary side of the step-up current transformer. The voltage limiter is a bi-directional zener diode. The high-voltage module enables independent brightness control for each gas discharge tube. The high-voltage module enables the same brightness for all gas discharge tubes in the system. The same high-voltage module can support gas discharge tubes of varying length.
The high-voltage module is constructed and arranged to occupy a relatively small volume and thus may be mounted next to the gas discharge tube within a letter enclosure. The high-voltage module is also constructed and arranged to have a relatively low weight. Due to the small size and low weight, the high-voltage module may be used within small letters or may be used with letters and signs having complex shapes.
According to yet another aspect, a system for providing electrical power to several gas discharge tubes includes a master power supply constructed and arranged to provide high-frequency and low-voltage power via standard electrical wires to several high-voltage modules. Each high-voltage module includes a step-up transformer constructed to receive high-frequency and low-voltage power at the primary side of the step-up transformer. The high-voltage module provides, in turn, high-frequency and high-voltage power from the secondary side of the step-up transformer to electrodes of one gas discharge tube via high-voltage wires. The individual high-voltage modules have their primary sides connected in series to the master power supply. The master power supply includes a fault detector arranged to receive a signal from a fault feedback circuit provided in each high-voltage module.
The master power supply may include a ground fault detector arranged to receive a signal from a ground fault feedback circuit provided in the high-voltage module. The ground fault detector may be a secondary ground fault level sensor constructed to sense a leakage current from the high-voltage module. The master power supply may include an inverter fail detector constructed to monitor ground connection between the high-voltage module and the power supply. The inverter fail detector may be constructed to monitor operation of a power inverter of the power supply.
The master power supply may include an open circuit detector constructed to sense an overload in the high-voltage module. The open circuit detector may be constructed to sense the overload by detecting a high-frequency current of a non-sinusoidal waveform received from the high-voltage module having a diode connected across the primary side of the step-up transformer. The master power supply may include a line over voltage detector constructed to detect a threshold value of a line voltage.
The above-designs provide novel systems that afford a high degree of safety and satisfy safety requirements of different countries (e.g., in the U.S. satisfy UL 2161, which are incorporated by reference) The novel system may be used as a highly flexible channel letter system that can be installed at a lower cost than standard channel letter systems.